Prompt $\nu_{\tau}$ Fluxes in Present and Future Tau Neutrino Experiments

We use a non-perturbative QCD approach, the Quark Gluon String Model, to compute the $\tau$-neutrino fluxes produced by fixed target $p A$ collisions (where $A$ is a target material) for incident protons of energies ranging from 120 to 800 GeV. The purpose of this calculation is to estimate {\it in a consistent way \rm} the prompt background for the $\nu_\mu(\nu_e) \leftrightarrow \nu_\tau$ oscillation search in the on-going $\nu_\mu(\nu_e) \leftrightarrow \nu_\tau$ oscillation search experiments CHORUS and NOMAD, as well as the expected prompt background in future experiments, such as COSMOS at FNAL and a possible second-generation $\nu_\mu(\nu_e) \leftrightarrow \nu_\tau$ search experiment at the SPS. In addition, we compute the number of $\nu_\tau$ interactions expected by the experiment E872 at FNAL.